Tetrafluoroethylene-containing powder, process for making same, articles molded therefrom and compositions containing such powder

Abstract

A tetrafluoroethylene-containing powder contains free flowing particles of a tetrafluoroethylene polymer at least partially encapsulated by a polymer or copolymer selected from polystyrene, poly- alpha -alkylstyrenes, styrene-acrylonitrile copolymers, alpha -alkylstyrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-butadiene rubbers and their mixtures. The powder is obtained by emulsion polymerization of one or more monomers in the presence of a tetrafluoroethylene polymer and is useful as an additive in polymer compositions and in making molded articles.

We claim: 
     
       1. A tetrafluoroethylene polymer-containing powder, comprising: free-flowing particles, said particles comprising a tetrafluoroethylene polymer at least partially encapsulated by a polymer or copolymer selected from the group consisting of polystyrene, poly-α-alkylstyrenes, styrene-acrylonitrile copolymers, α-alkylstyrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-butadiene rubbers and their mixtures, wherein the encapsulating polymer or copolymer is obtained by emulsion polymerization of one or more monomers in the presence of a tetrafluoroethylene polymer latex. 
     
     
       2. A powder according to claim 1, wherein the encapsulation polymer or copolymer is selected from the group consisting of styrene-acrylonitrile copolymers, a-methylstyrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymers and their mixtures. 
     
     
       3. The powder according to claim 1, wherein the tetrafluoroethylene polymer represents 0.01 to 80% by weight with respect to the total weight of the polymers in the powder. 
     
     
       4. The powder according to claim 1, wherein the tetrafluoroethylene polymer represents 0.05 to 70% by weight with respect to the total weight of the polymers in the powder. 
     
     
       5. An article obtained by extrusion moulding, extrusion blow moulding or injection moulding of a powder according to claim 1. 
     
     
       6. A composition, comprising: a polymer matrix and a tetrafluoroethylene polymer-containing powder according to claim 1 dispersed in the polymer matrix, wherein the polymer matrix is selected from the group consisting of polycarbonate resins, acrylonitrile-butadiene-styrene copolymers and mixtures thereof and wherein the tetrafluoroethylene polymer content in the composition is from 0.05 to 10 parts by weight tetrafluoroethylene polymer per 100 parts by weight of the polymer matrix. 
     
     
       7. Article obtained by extrusion moulding, extrusion blow moulding or injection moulding of a composition according to claim 6. 
     
     
       8. A process for making a tetrafluoroethylene polymer-containing powder, comprising: emulsion-polymerizing a monomer or mixture of monomers in the presence of a tetrafluoroethylene polymer latex to form particles, said particles comprising the tetrafluoroethylene polymer encapsulated in a polymer or copolymer selected from the group consisting of polystyrene, poly-α-alkylstyrenes, polybutadienes, styrene-acrylonitrile copolymers, α-alkylstyrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene copolymers, styrene-butadiene rubbers and their mixtures; and recovering the particles in the form of the free-flowing tetrafluoroethylene polymer-containing powder. 
     
     
       9. Process according to claim 8, wherein the emulsion polymerization is carried out by radical route. 
     
     
       10. A tetrafluoroethylene polymer-containing powder made by the process of claim 8. 
     
     
       11. The powder of claim 10, wherein the particles of the powder comprise a tetrafluoroethylene polymer encapsulated in a styrene-acrylonitrile copolymer, an acrylonitrile-butadiene-styrene copolymer, an α-methylstyrene-acrylonitrile copolymer or a mixture thereof. 
     
     
       12. A composition, comprising: a polymer matrix and a tetrafluoroethylene polymer-containing powder made by the process of claim 11 dispersed in the polymer matrix, wherein the polymer matrix is selected from the group consisting of polycarbonate resins, acrylonitrile-butadiene-styrene copolymers and mixtures thereof and wherein tetrafluoroethylene polymer content in the composition is from 0.05 to 10 parts by weight per 100 parts by weight of the polymer matrix.